Methods for compensating for thermal expansion during additive manufacturing

ABSTRACT

Embodiments of the present disclosure are drawn to additive manufacturing apparatus and methods. An exemplary additive manufacturing method may include forming a part using additive manufacturing. The method may also include bringing the part to a first temperature, measuring the part along at least three axes at the first temperature, bringing the part to a second temperature, different than the first temperature, and measuring the part along the at least three axes at the second temperature. The method may further include comparing the size of the part at the first and second temperatures to calculate a coefficient of thermal expansion, generating a tool path that compensates for the coefficient of thermal expansion, bringing the part to the first temperature, and trimming the part while the part is at the first temperature using the tool path.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. application Ser.No. 15/636,789, filed Jun. 29, 2017, now U.S. Pat. No. 9,833,986, theentirety of which is herein incorporated by reference.

TECHNICAL FIELD

Aspects of the present disclosure relate to apparatus and methods forfabricating components (such as, e.g., automobile parts, medicaldevices, machine components, consumer products, etc.) via additivemanufacturing techniques or processes. Such processes include, e.g.,three-dimensional (3D) printing manufacturing techniques or processes.

BACKGROUND

Additive manufacturing techniques and processes generally involve thebuildup of one or more materials, e.g., layering, to make a net or nearnet shape (NNS) object, in contrast to subtractive manufacturingmethods. Though “additive manufacturing” is an industry standard term(ASTM F2792), additive manufacturing encompasses various manufacturingand prototyping techniques known under a variety of names, including,e.g., freeform fabrication, 3D printing, rapid prototyping/tooling, etc.Additive manufacturing techniques may be used to fabricate simple orcomplex components from a wide variety of materials. For example, afreestanding object may be fabricated from a computer-aided design (CAD)model.

A particular type of additive manufacturing is more commonly known as 3Dprinting. One such process, commonly referred to as Fused DepositionModeling (FDM), comprises a process of melting a thin layer of aflowable material (e.g., a thermoplastic material), and applying thismaterial in layers to produce a final part. This is commonlyaccomplished by passing a continuous, thin filament of thermoplasticmaterial through a heated nozzle, which melts the thermoplastic materialand applies the material to the structure being printed, building up thestructure. The heated material is applied to the existing structure inthin layers, melting and fusing with the existing material to produce asolid finished product.

The filament used in the aforementioned process is generally producedusing a plastic extruder, which may be comprised of a specially designedsteel screw rotating inside a heated steel barrel. Thermoplasticmaterial in the form of small pellets is introduced into one end of therotating screw. Friction from the rotating screw, combined with heatfrom the barrel, softens the plastic, which may be then forced underpressure through a small opening in a die attached to the front of theextruder barrel. This extrudes a string of material, which may be cooledand coiled up for use in the 3D printer.

Melting a thin filament of material in order to 3D print an item may bea slow process, which may only be suitable for producing relativelysmall items, or a limited number of items. As a result, the meltedfilament approach to 3D printing may be too slow for the manufacture oflarge items, or a larger numbers of items. However, 3D printing usingmolten thermoplastic materials offers advantages for the manufacture oflarge items or a large number of items.

A common method of additive manufacturing, or 3D printing, generallyincludes forming and extruding a bead of flowable material (e.g., moltenthermoplastic), applying the bead of material in a strata of layers toform a facsimile of an article, and machining the facsimile to producean end product. Such a process is generally achieved by means of anextruder mounted on a computer numeric controlled (CNC) machine withcontrolled motion along at least the x-, y-, and z-axes. In some cases,the flowable material, such as, e.g., molten thermoplastic material, maybe infused with a reinforcing material (e.g., strands of fiber or othersuitable material or combination of materials) to enhance the material'sstrength.

The flowable material, while generally hot and pliable, may be depositedupon a substrate (e.g., a mold), pressed down or otherwise flattened tosome extent, and/or leveled to a consistent thickness, preferably bymeans of a compression roller mechanism. The compression roller may bemounted in or on a rotatable carrier, which may be operable to maintainthe roller in an orientation tangential, e.g., perpendicular, to thedeposited material (e.g., bead or beads of thermoplastic material). Theflattening process may aid in fusing a new layer of the flowablematerial to the previously deposited layer of the flowable material. Insome instances, an oscillating plate may be used to flatten the bead offlowable material to a desired thickness, thus effecting fusion to thepreviously deposited layer of flowable material. The deposition processmay be repeated so that successive layers of flowable material aredeposited upon an existing layer to build up and manufacture a desiredcomponent structure. When executed properly, the new layer of flowablematerial may be deposited at a temperature sufficient enough to allowthe new layer of material to melt and fuse with a previously depositedlayer, thus producing a solid part.

In some instances, the process of 3D-printing a part, which may utilizea large print bead to achieve an accurate final size and shape, mayinvolve a two-step process. This two-step process, commonly referred toas near-net-shape, may begin by printing a part to a size slightlylarger than needed, then machining, milling, or routing the part to thefinal size and shape. The additional time required to trim the part tofinal size may be compensated for by the faster printing process.

One desirable application for large-scale 3D printed parts is in thefabrication of molds and/or tooling, commonly used to manufacturecomponents from thermoset materials, e.g., fiber reinforced epoxy atelevated temperatures in an autoclave. Such components are often desiredin the manufacture of aircraft and aerospace products. Traditionalmethods of fabricating these tools may be lengthy, complex, cumbersome,and/or expensive. Tools made from a reinforced flowable material (e.g.,a fiber reinforced thermoplastic material) capable of withstanding anyprocess temperatures required are desirable. Tools manufactured this waymay be manufactured faster and at a lower cost. One example of athermoplastic material suitable for the aforementioned application ispolyphenylene sulfide, (“PPS”).

PPS, along with numerous other fiber-reinforced thermoplastics, althoughsuitable for a high-temperature operating environment, may exhibit otherphysical characteristics, which may need to be considered in order to beusable for the aforementioned tools and/or molds. For example, PPSexpands in physical size as it is heated and contracts again whencooled. Another characteristic of PPS that may further complicate itsuse is that material printed using a 3D printer may not expand andcontract at the same rate in all directions. During the printingprocess, the reinforcing fibers may tend to align themselves with adirection of polymer flow, which may result in some reinforcing fibersbeing aligned along the direction of the printed bead of a flowablematerial (e.g., printed thermoplastic material). As a result, theprinted polymer bead may tend to expand and contract at a slower rate inthe direction of the reinforcing fibers and at a faster rate in adirection transverse to the bead length. This may be further complicatedby the fact that different methods of printing may result in differentfiber orientation within the print bead itself, and different parts maybe printed using different patterns and orientations of print bead.

In the practice of the aforementioned additive manufacturing processes,some disadvantages have been encountered. Thermoplastic tools and moldsmay expand and contract with changes in temperature. However, the amountof expansion and contraction may vary in different directions of aprinted bead of material. Owing to variations in the print process andvariations in the fiber orientation of the print bead(s), it may bedifficult to predict the amount of expansion and contraction of aparticular printed part (e.g., a tool or a mold) when exposed totemperature variations.

SUMMARY

Aspects of the present disclosure relate to, among other things, methodsand apparatus for fabricating components via additive manufacturing,such as, e.g., 3D printing techniques. Each of the aspects disclosedherein may include one or more of the features described in connectionwith any of the other disclosed aspects.

An object of the present invention is to establish a process by which 3Dprinted parts (e.g., tools and/or molds) may be fabricated using a nearnet shape additive manufacturing process so that when heated to aspecific process temperature, the 3D printed parts may expand to acorrect size and/or shape. To accomplish this, first, the rate ofthermal expansion of the part (e.g., a tool or a mold) may be determinedin each direction. Second, the thermal expansion information may be usedto modify the original CNC trimming program, which may then be used totrim the tool and/or mold a second time. In doing so, the size and shapeof the resulting part may be reduced in one or more directions by anamount appropriate to allow for thermal expansion.

In one aspect of the disclosure, the process begins by 3D printing therequired tool or mold and subsequently machining and trimming the toolor mold to the specified size at room temperature. A touch probe may bemounted to the subtractive (or trimming) gantry, for example, to thetrim spindle of the gantry. The touch probe may have an accuracy in therange of, e.g., 0.001″ or less. While at room temperature, a CNC programmay be executed to touch the touch probe to the printed part todetermine the size of the part at several locations, e.g., along each ofthree perpendicular axes. Once the size of the part at the variouspoints is measured, the information may be stored in the control memoryof the CNC machine.

In a next step, the machined tool or mold may be heated to the properprocess temperature at which the tool or mold is intended to be heatedto during use. The process temperature may range from 200 degrees to 450degrees Fahrenheit. The tool or mold may be returned to the machine (oralternatively the tool or mold may have been heated while remaining inthe machine), where the machined tool or mold is again measured, forexample, using the same measurement CNC program used previously.Measurements may again be taken, e.g., along each of the threeperpendicular axes, and the additional measurement information may bestored in the control memory.

Based on the measurements, the amount that the part expands per unit ofmeasure with a specific rise in temperature can be calculated, forexample, in units of expansion per inch per degree Fahrenheit. Thisnumber is commonly referred to as the Coefficient of Thermal Expansion(“CTE”). Due to variations in the expansion of the print bead due tofiber orientation and the variable pattern of the print bead in aparticular part, it is normal for the CTE number to be different alongdifferent perpendicular axes of a part.

To compensate for thermal expansion, the part may be re-sized and/orre-shaped to account for any thermal expansion that may occur when thepart is heated to a process temperature during use. To adjust the shapeand/or size of the part to account for thermal expansion, the part mayfirst be aligned with the axes of the machine, and the CTE of the partmay be determined along each axis of motion of the machine. In a nextstep, the motion of the machine may be adjusted so that when the CNCprogram is executed, the motion of each axis of the machine is adjustedto accommodate the thermal expansion. Accordingly, instead of moving thedistance instructed by the original CNC program (as may have occurredwhen the part was initially trimmed), the movement of the machine alongeach increment of motion is adjusted to adapt for the CTE along thataxis of motion. This compensates for the temperature rise from theambient temperature at which the part is machined, to the processtemperature at which it will be used. For example, tools or molds may bemachined so that when the tools or the molds are used, their thermalexpansion may be accounted for. In this way, the original part CNCprogram may be used, and the CNC machine control may make adjustments tothe part size/shape to allow for thermal expansion.

An advantage of this type of modification process is if the ambienttemperature at which the part is ultimately machined is different thanthe machining temperature that was expected when the tool path for thepart was programmed, it may not be necessary to reprogram the part forthe actual machining temperature. Moreover, the printing and/or trimmingprocess may extend over a longer period of time, during which theambient temperature of the room and the temperature of the part beingmachined may change. By utilizing the above-identified approach, the CNCmachine control may continuously and/or periodically monitor thetemperature of the room and the temperature of the part being machined,and may continuously or periodically adjust the amount by which themachine compensates along each axis based on current temperatures.

In one aspect of the disclosure, the CNC machine control may compensatefor temperature variations as described above in several ways. Forexample, one way may include adjusting the scaling for each axis, whichmay define how much machine motion is generated for a specific rotationof the servo drive. By adjusting the scaling, the machine may move adifferent amount for each rotation of the drive than it normally would(e.g., it may move more or less) to adjust the overall motion of themachine and provide compensation for expansion. In another example, aspecific calculated distance for each increment of programmed motion maybe added or subtracted along each axis. In an exemplary embodiment, asoftware compensation table may be created, which may define theposition of each axis desired for each programmed position along thataxis. Indeed, a number of different methods or combinations of methodsmay be used to adjust the motion of the machine to compensate for CTE.Regardless of which method may be selected, the control may execute theCNC trimming program a second time so that when heated to the processtemperature, the part is the correct shape and size.

In another aspect of the disclosure, scanning technology may be used tomeasure the size of the part at room temperature and at the processtemperature. For example, the process may begin by 3D printing therequired tool or mold and subsequently machining and trimming the toolor mold to the specified size at room temperature. While at roomtemperature, one or more surfaces of the part may be scanned withsurface scanning technology, such as a laser scanner or ultrasoundscanner, to generate a software representation of the part's surface.The software representation may be stored as computer data. In someembodiments, a computer design surface or solid representation of thepart may be used. The computer design surface or solid representationmay correspond to surface(s), and/or dimensions, of a hypotheticaldesired part using computer-aided design software. In a next step, themachined tool or mold may be heated to the proper process temperature atwhich the tool or mold is intended to be heated to during use. One ormore surfaces of the part may then be re-scanned while the part is atthe process temperature, another software representation or a computerdesign surface may be generated, and this additional information may bestored.

Computer software may then be used to determine the distance that pointson the tool surface expanded or moved in a direction perpendicular tothe surface. Based on this information, the software may then be used tocreate a tool surface that is the same perpendicular distance from theinitial surface at the various points, but in the opposite direction.This generates a software surface that is a shrunken version of theoriginal tool surface by an amount equal to the amount that the toolexpanded at the various points when heated to its process temperature.This new, shrunken, software surface is then used to generate a CNC toolpath that will then be used to machine the part to a size and shape thatwill expand to the required dimensions when heated to the processtemperature.

Embodiments of the present disclosure may be drawn to additivemanufacturing methods. An additive manufacturing method may includeforming a part using additive manufacturing and then bringing the partto a first temperature. The method may also include measuring the partalong at least three axes while the part is at the first temperature todetermine a size of the part at the first temperature along the at leastthree axes. The method may then include bringing the part to a secondtemperature, different than the first temperature, and measuring thepart along the at least three axes while the part is at the secondtemperature to determine a size of the part at the second temperaturealong the at least three axes. The method may further include comparingthe size of the part at the first temperature and the size of the partat the second temperature along the at least three axes to calculate acoefficient of thermal expansion per a unit of measure per a unit oftemperature change. The method may then include generating a tool paththat compensates for the coefficient of thermal expansion, bringing thepart to the first temperature, and trimming the part while the part isat the first temperature using the tool path that compensates for thecoefficient of thermal expansion.

In another embodiment of the present disclosure, an additivemanufacturing method may include printing a part using athree-dimensional printer, and bringing the part to a first temperature.The method may also include measuring the part along a plurality of axeswhile the part is at the first temperature to determine a size of thepart at the first temperature using a surface scanner or a touch probe,and transmitting measurement data from the surface scanner or the touchprobe to a controller. The method may then include heating the part to asecond temperature, greater than the first temperature, and measuringthe part along the plurality of axes while the part is at the secondtemperature to determine a size of the part at the second temperatureusing the surface scanner or the touch probe. The method may theninclude transmitting measurement data from the surface scanner or thetouch probe to the controller, and comparing the size of the part at thefirst temperature and the size of the part at the second temperature andcalculating a coefficient of thermal expansion per a unit of measure pera unit of temperature change using the controller. The method mayfurther include generating a tool path that compensates for thecoefficient of thermal expansion, bringing the part to the firsttemperature, and trimming the part while the part is at the firsttemperature using the tool path that compensates for the coefficient ofthermal expansion.

In another embodiment of the present disclosure, an additivemanufacturing method may include forming a part using a computer numericcontrolled machine, cooling the part to a room temperature, and trimmingthe part while the part is at the room temperature. The method may alsoinclude measuring the part, once trimmed, while the part is at the roomtemperature to determine a size of the part at the room temperaturealong a plurality of axes. The method may then include heating the partto a second temperature, higher than the first temperature, andmeasuring the part while the part is at the second temperature todetermine a size of the part at the second temperature along theplurality of axes. The method may further include comparing the size ofthe part at the first temperature and the size of the part at the secondtemperature along the plurality of axes to calculate a coefficient ofthermal expansion per a unit of measure per a unit of temperaturechange, and generating a tool path that compensates for the coefficientof thermal expansion. The method may next include cooling the part tothe room temperature, and trimming the cooled part using the tool paththat compensates for the coefficient of thermal expansion.

As used herein, the terms “comprises,” “comprising,” or any othervariation thereof, are intended to cover a non-exclusive inclusion, suchas a process, method, article, or apparatus. The term “exemplary” isused in the sense of “example,” rather than “ideal.”

It may be understood that both the foregoing general description and thefollowing detailed description are exemplary and explanatory only andare not restrictive of the disclosure, as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate exemplary aspects of the presentdisclosure and together with the description, serve to explain theprinciples of the disclosure.

FIG. 1 is a perspective view of an exemplary CNC machine operablepursuant to an additive manufacturing process in forming articles,according to an aspect of the present disclosure;

FIG. 2 is an enlarged perspective view of an exemplary carrier andapplicator assembly of the exemplary CNC machine shown in FIG. 1;

FIG. 3A is an enlarged cross-sectional view of an exemplary applicatorhead assembly shown in FIG. 2, during use;

FIG. 3B is a top view of an exemplary layer of flowable materialcontaining reinforcing fibers;

FIG. 4A is a perspective view of an exemplary part formed by additivemanufacturing;

FIG. 4B is a perspective view of the exemplary part in FIG. 4A, trimmedto a desired shape and size;

FIG. 5 is a perspective view of the exemplary trimmed part in FIG. 4Bbeing measured by an exemplary probing technology attached to anexemplary trimming gantry;

FIG. 6 is a perspective view of the exemplary trimmed part in FIG. 4Bbeing measured by an exemplary scanning technology attached to anexemplary trimming gantry;

FIG. 7 is a flowchart depicting steps of an exemplary method, accordingto an aspect of the present disclosure; and

FIG. 8 is a flowchart depicting steps of an exemplary method, accordingto an aspect of the present disclosure.

DETAILED DESCRIPTION

The present disclosure is drawn to, among other things, methods andapparatus for fabricating components via additive manufacturing or 3Dprinting techniques. More particularly, the methods and apparatusdescribed herein comprise a method for fabricating printed parts (e.g.,tools, molds, etc.) using a near net shape additive manufacturingprocess so that when the printed part is heated to a specific processtemperature, the part may expand to a correct size and shape.

For purposes of brevity, the methods and apparatus described herein willbe discussed in connection with the fabrication of parts usingthermoplastic materials. However, those of ordinary skill in the artwill readily recognize that the disclosed apparatus and methods may beused with any flowable material suitable for additive manufacturing,such as, e.g., 3D printing.

With reference now to FIG. 1, there is illustrated a CNC machine 1embodying aspects of the present disclosure. A control/controller (notshown) may be operatively connected to CNC machine 1 for displacing anapplication nozzle 51 along a longitudinal line of travel (x-axis), atransverse line of travel (y-axis), and a vertical line of travel(z-axis), in accordance with a program inputted or loaded into thecontroller for performing an additive manufacturing process to form adesired component. CNC machine 1 may be configured to print or otherwisebuild 3D parts from digital representations of the 3D parts (e.g., AMFand STL format files) programmed or loaded into the controller.

For example, in an extrusion-based additive manufacturing system, a 3Dpart may be printed from a digital representation of the 3D part in alayer-by-layer manner by extruding a flowable material. The flowablematerial may be extruded through an extrusion tip or nozzle 51 carriedby a print head or an applicator head 43 of the system. The flowablematerial may be deposited as a sequence of beads or layers on asubstrate in an x-y plane. The extruded, flowable material may fuse topreviously deposited material and may solidify upon a drop intemperature. The position of the print head relative to the substratemay then be incrementally advanced along a z-axis (perpendicular to thex-y plane), and the process may then be repeated to form a 3D partresembling the digital representation.

CNC machine 1, shown in FIG. 1, includes a bed 20 provided with a pairof transversely spaced side walls 21 and 22, a printing gantry 23, and atrimming gantry 36 supported on one or more of side walls 21 and 22. CNCmachine 1 also includes a carriage 24 mounted on printing gantry 23, acarrier 25 mounted on carriage 24, an extruder 61, and an applicatorassembly 43 mounted on carrier 25. Located on bed 20 between side walls21 and 22 is a worktable 27 provided with a support surface. Worktable27 may be horizontal. The support surface may be disposed in an x-yplane and may be fixed or displaceable along an x-axis or a y-axis. Inan example, displacement of worktable 27 may be achieved using one ormore servomotors and one or more of rails 28 and 29 mounted on bed 20and operatively connected to worktable 27. Printing gantry 23 andtrimming gantry 36 are disposed along a y-axis, supported on side walls21 and 22. Printing gantry 23 and trimming gantry 36 may be mounted on aset of guide rails 28, 29, which are located along a top surface of sidewalls 21 and 22. Both printing gantry 23 and trimming gantry 36 mayeither be fixedly or displaceably mounted, and, in some aspects,printing gantry 23 and trimming gantry 36 may be displaced along thex-axis. In an exemplary displaceable version, one or more servomotorsmay control movement of printing gantry 23 and/or trimming gantry 36.For example, one or more servomotors may be mounted on printing gantry23 and/or trimming gantry 36 and operatively connected to tracks, e.g.,guide rails 28, 29, provided on side walls 21 and 22 of bed 20.

Carriage 24 may be supported on printing gantry 23 and may be providedwith a support member 30 mounted on and displaceable along one or moreguide rails 31, 32, and 33 provided on the printing gantry 23. Carriage24 may be displaceable along a y-axis on one or more guide rails 31, 32,and 33 by a servomotor mounted on printing gantry 23 and operativelyconnected to support member 30. Carrier 25 is mounted on one or morevertically disposed guide rails 35 supported on carriage 24 fordisplacement of carrier 25 relative to carriage 24 along a z-axis.Carrier 25 may be displaceable along a z-axis by one or more servomotorsmounted on carriage 24 and operatively connected to carrier 25.

As best shown in FIG. 2, mounted to carrier 25 is a positivedisplacement gear pump 62, which may be driven by a servomotor 63through a gearbox 64. Gear pump 62 receives molten plastic from extruder61, shown in FIG. 1. A compression roller 59 (e.g., bead shaping roller)for compressing material may be mounted on carrier bracket 47.Compression roller 59 may be moveably mounted on carrier bracket 47, forexample, rotatably or pivotably mounted. Compression roller 59 may bemounted relative to nozzle 51 so that material, e.g., one or more beadsof flowable material (such as thermoplastic resin), discharged fromnozzle 51 is smoothed, flattened, leveled, and/or compressed bycompression roller 59, as depicted in FIG. 3A. One or more servomotors60 may be configured to move, e.g., rotationally or pivotably displace,carrier bracket 47 via a pulley 56 and belt 65 arrangement. In someexamples, carrier bracket 47 may be rotationally or pivotably displacedvia a sprocket and drive-chain arrangement.

With reference to FIG. 3A, applicator head 43 may include a housing 46with a roller bearing 49 mounted therein. Carrier bracket 47 may bemounted, e.g., fixedly mounted, to an adaptor sleeve 50, journaled inbearing 49. As shown in FIG. 3A, a bead of a flowable material 53 (e.g.,a thermoplastic material) under pressure from a source disposed oncarrier 25 (e.g. gear pump) or another source (e.g., one or moreextruder 61 (FIG. 1) and an associated polymer or gear pump) disposed oncarrier 25 may be flowed to applicator head 43, which may be fixedly (orremovably) connected to, and in communication with, nozzle 51. In use,flowable material 53 (e.g., thermoplastic material) may be heatedsufficiently to form a molten bead thereof, and may be extruded throughnozzle 51 to form multiple rows of deposited material 52 onto a surfaceof worktable 27. In some embodiments, flowable material 53 may include asuitable reinforcing material, such as, e.g., fibers, that facilitateand enhance the fusion of adjacent layers of extruded flowable material53. In some aspects, flowable material 53 delivered onto a surface ofworktable 27 may be free of trapped air, the rows of deposited materialmay be uniform, and/or the deposited material may be smooth. Forexample, flowable material 53 may be flattened, leveled, and/or fused toadjoining layers by any suitable means (e.g., compression roller 59), toform an article.

Although compression roller 59 is depicted as being integral withapplicator head 43, compression roller 59 may be separate and discretefrom applicator head 43. In some embodiments, compression roller 59 maybe removably mounted to machine 1. For example, different sized orshaped compression rollers 59 may be interchangeably mounted on machine1, depending, e.g., on the type of flowable material 53 and/or desiredcharacteristics of the rows of deposited flowable to be formed onworktable 27.

In an example, machine 1 may also include a velocimetry assembly (ormultiple velocimetry assemblies) configured to determine flow rates(e.g., velocities and/or volumetric flow rates) of deposited flowablematerial 53 being delivered from applicator head 43. The velocimetryassembly may transmit signals relating to the determined flow rates tothe aforementioned controller coupled to machine 1, which then mayutilize the received information to compensate for variations in thematerial flow rates.

In the course of fabricating a component, pursuant to the methodsdescribed herein, the control system of machine 1, in executing theinputted program, may operate the several servomotors as described todisplace printing gantry 23 and trimming gantry 36 along the x-axis,displace carriage 24 along the y-axis, displace carrier 25 along thez-axis, and/or rotate carrier bracket 47 about the z-axis while nozzle51 deposits flowable material 53 and compression roller 59 compressesthe deposited material, as shown in FIG. 3A.

FIG. 3B shows a top view of an exemplary irregularly shaped layer ofdeposited flowable material 53 containing reinforcing fibers 80. Duringoperation of machine 1 (i.e., during the printing process), reinforcingfibers 80 may align themselves along a direction of flow as material isdeposited by nozzle 51. This generally results in reinforcing fibersaligned along the direction of the deposition of flowable material. Forexample, on the left side of FIG. 3B, flowable material was deposited bynozzle 51 in a direction 81. Accordingly, reinforcing fibers 80 are alsoaligned along direction 81. On the right side of FIG. 3B, flowablematerial was deposited in a serpentine shape. Accordingly, reinforcingfibers 80 are aligned in a serpentine shape, curving back and forthbetween a direction 82 and direction 81, which are perpendicular to oneanother.

As a result of the different orientations of reinforcing fiberalignment, a bead of deposited flowable material 53 may tend to expandand contract at a slower or faster rate in different directions. Forexample, once hardened, flowable material 53 may expand and contract ata slower rate in the direction in which reinforcing fibers 80 areoriented. Using the left side of FIG. 3B as an example, hardenedflowable material 53 may expand and contract more slowly in direction 81and may expand and contract at a faster rate in direction 82, transverseto the orientation of reinforcing fibers 80 (i.e., direction 81).Although this straightforward example is used for simplicity, it isacknowledged that different methods of deposition (e.g., 3D printing)may also result in different fiber orientations within the depositedflowable material 53. Accordingly, the type of 3D printing used and thedirection of deposition may both affect the orientation of reinforcementfibers. Additionally, some parts made using additive manufacturing mayalso utilize different deposition patterns and/or orientations of a beadof deposited flowable material 53, which may result in furtherirregularity in the alignment of reinforcing fibers 80 in the hardened,formed part.

During operation of machine 1 to form a part, the deposition process maybe repeated so that each successive layer of flowable material 53 may bedeposited upon an existing layer to build up and manufacture a desiredprinted part 55, as shown in FIG. 4A. Part 55 may be comprised ofmultiple rows of deposited flowable material laid successively on asurface of worktable 27, as described and shown in FIG. 3A. In someembodiments, printed part 55 may be allowed to cool down for apredetermined period of time (e.g., several minutes to several hours,depending, e.g., on the type of thermoplastic material used) to reachroom temperature before any machining and/or trimming operationscommence.

Once part 55 has cooled to room temperature, trimming gantry 36 may beused with an attached router to machine and/or trim printed part 55 to afinal net shape 57, as shown in FIG. 4B. Initially, a first pass (e.g.,roughing pass) may be performed by trimming gantry 36 with the attachedrouter to remove a first portion of material (e.g., a first roughingpass to remove most excess material). Subsequently, a second pass may beperformed, if necessary, by trimming gantry 36 to produce a smoothsurface on final net shape part 57, as shown in FIG. 4B. In someexamples, additional passes may be executed by trimming gantry 36 if thenet shape of final part 57 is not of a desirable shape, size,smoothness, or other suitable property. In other aspects, a single passmay be used to form the net shape of final part 57.

When final net shape part 57 is completed on worktable 27, in a nextstep, a touch probe 67 may be attached to trimming gantry 36, as shownin FIG. 5. Touch probe 67 may be attached to a spindle of machine 1(e.g., a spindle of trimming gantry 36) in such a manner that thecontrol of machine 1 may know the precise position of a tip of the touchprobe with respect to a position of machine 1. Machine 1 may then movetowards a part to be measured. In an exemplary embodiment, touch probe67 may include a highly accurate switch that may trip when touch probe67 comes in contact with part 57. When the switch of touch probe 67trips, the control of machine 1 may note the exact position of the tipof touch probe 67 in order to provide an accurate measurement of part57. In some examples, touch probe 67 may be highly accurate and may havea measurement accuracy of 0.001″ to 0.0001″ to obtain highly accuratemeasurements of final net shape part 57. In an exemplary embodiment,touch probe 67 may be configured to create a plurality of measurementpoints on part 57, under the control, e.g., of a CNC program. The CNCprogram may be programmed in advance of any machining, trimming, orother post-printing process steps, or during or after such steps. Insome aspects, the measurement points obtained using touch probe 67 maybe controlled manually rather than by a CNC program.

Alternatively, in another exemplary embodiment, when final net shapepart 57 is completed on worktable 27, a surface scanner 68 may beattached to trimming gantry 36, as shown in FIG. 6. Surface scanner 68may be used to create a three-dimensional (3D) surface scan of finalpart 57. During operation, trimming gantry 36 may move around part 57 tocreate a complete 3D image of part 57. For example, trimming gantry 36and surface scanner 68 may move 360 degrees around part 57 and may makeone or more revolutions around part 57. Trimming gantry 37 and surfacescanner 68 may also move over the top of part 57. In some examples,surface scanner 68 may be highly accurate and may be configured toobtain highly accurate measurements of final net shape part 57. Forexample, in some embodiments, surface scanner 68 may obtain measurementsfrom 0.002″ to 0.0001″. In an exemplary embodiment, similarly to touchprobe 67, surface scanner may be used to create a number of measurementpoints on part 57 as trimming gantry 37 moves under the control of a CNCprogram. In some embodiments, surface scanner 68 may be used to generatea 3D rendition of part 57 that reflects these measurements usingsuitable software. The CNC program used to move surface scanner 68 maybe programmed in advance of any machining, trimming, or otherpost-printing process steps, or during or after such steps. In someaspects, the measurement points obtained using surface scanner 68 may becontrolled manually rather than by a CNC program.

Any suitable surface scanning technology may be used to measure part 57.For example, ultrasonic or ultrasound scanning may be used to detectpart 57 and measure distances, or laser scanning technology may be used.In an exemplary embodiment, surface scanner 68 may not be attached totrimming gantry 37 and may instead be a hand-held scanner that may beused by an operator to create a 3D image of final part 57.

During operation of machine 1, trimming gantry 36 may move around part57, and/or may move over one or more surfaces of part 57, to create amatrix of data, e.g., size data, about part 57 in an initial datacollection step. Measurements of part 57 may then be taken again in asubsequent measurement step, once part 57 has been heated up to asecond, process temperature, warmer than the temperature of part 57during the initial measuring step. In exemplary embodiments, the initialtemperature of part 57 may be in the range of, e.g., 60 degrees to 100degrees Fahrenheit, and the process temperature may be in the range of,e.g., 200 degrees to 450 degrees Fahrenheit.

In some embodiments, measurements may first be taken at the initialprocess temperature, and then part 57 may be cooled to a second, lower,temperature for taking a second set of measurements. In some aspects,part 57 may be measured at more than two different temperatures.

At a next step, the control of machine 1 may then compare the two (ormore) sets of measurement data and may use the comparison data togenerate a new tool path. Suitable software may be stored in the controlof machine 1 to perform the steps disclosed herein. The control ofmachine 1 may perform this function by subtracting the initialmeasurements at each measurement point taken when part 57 was at acooler temperature from measurements taken at each measurement pointwhen part 57 was then heated to a process temperature to determine theamount of expansion at each measurement point. This expansion amount maythen be divided by the initial size measurement at each measurementpoint to calculate the expansion per unit of measure, for example, theexpansion per inch. This expansion per unit of measure may then bedivided by the number of units of temperature difference between theroom temperature at which the initial measurements were taken and theelevated, process temperature at which the second set of measurementswere taken (or vice versa, if the elevated temperature measurements weretaken first). The result of these calculations is the rate of expansionper unit of measure per unit of temperature change, for example,expansion per inch per degree Fahrenheit. This may be referred to as theCoefficient of Thermal Expansion (“CTE”). In some aspects, to determinean average CTE of a part (e.g., tool or mold) in each of the threemutually perpendicular directions, the CTE number for each measurementalong each axis may be averaged.

The CTE of each axis, along with the temperature at which the part(e.g., tool or mold) may be used, may be stored in the machine CNCcontrol, for example, in a memory of the control. The CNC control maythen be instructed to run a second trimming program taking into accountthe above CTE information. There are multiple techniques by which thiscan be accomplished by the machine CNC control. One technique mayinclude having a scaling factor on the machine that defines the amountof machine motion in each axis that results from rotation of the servodrive motor for that axis. This scaling factor may be adjusted so thatthe actual machine motion is increased or decreased to account for theCTE of the part along each machine axis. Another technique may includeadjusting the length of each motion along each axis to account for theCTE along that axis. Yet another technique may include generating a CNCprogram to run in the background that modifies the program motions toaccount for the CTE variation along each machine axis. One of skill inthe art will understand that the above list of compensation techniquesis exemplary only and is not exhaustive. Additionally, in someembodiments, a combination of techniques may be used. Once a techniqueis determined, the new tool path would then be used to trim the part asecond time while the part is at room temperature.

FIG. 7 depicts an exemplary method of using a touch probe to generate anew tool-path program to compensate for CTE. The exemplary method beginsat a starting step 70, during which an initial part 55 (e.g.,thermoplastic tool or mold) may be formed via additive manufacturing.Part 55 may be printed using printing gantry 23 of the CNC machine 1, asdescribed above. The exemplary method may utilize a tool-path programused for additive manufacturing using suitable software, for example,CAD software, to manufacture part 55. In some embodiments, part 55 maybe printed at room temperature.

Once part 55 is printed, at a step 71, part 55 may be cooled orotherwise brought to room temperature, if it is not already at roomtemperature, and trimmed using trimming gantry 36 to create a trimmedprinted part 57. At a step 72, trimmed part 57 may be probed with anappropriate surface probing technology (e.g., probe 67) at roomtemperature to measure trimmed part 57 along a plurality of axes. Themeasurement data may be transmitted from probe 67 to a control (notillustrated) for storage. At a next step 73, trimmed part 57 may then beheated (e.g., using an oven, one or more heat lamps or heaters, or othersuitable heating device) to bring part 57 up to a desired processtemperature. Heating of trimmed part 57 may occur in place on CNCmachine 1, or trimmed part 57 may be moved for heating.

A process temperature is the temperature at which part 57, e.g., a 3Dprinted tool or mold, would normally operate at or near during use. Forexample, a 3D printed tool may heat up when it is being used and, as aresult, may expand during use. The process temperature may varydepending upon the size of the part, shape of the part, type ofthermoplastic material used in making the part, intended use of thepart, and/or any other properties that may affect thermal expansion ofthe part. An exemplary process temperature may be 200 degrees to 450degrees Fahrenheit.

In a next step 74, trimmed part 57 may be probed once more using probe67, while part 57 is at the process temperature. Measurement data forthe heated, trimmed part 57 may be transmitted from probe 67 to thecontrol.

At a next step 75, the two sets of measurement data may be compared, andthe comparison data may be used to create a new tool-path program. Insome embodiments, the control may compare the sets of measurement data.The control of machine 1 may perform this function by subtracting theinitial measurements at each measurement point taken when part 57 was ata cooler temperature from measurements taken at each measurement pointwhen part 57 was then heated to a process temperature to determine theamount of expansion at each measurement point. This expansion amount maythen be divided by the initial size measurement at each measurementpoint to calculate the expansion per unit of measure, for example, theexpansion per inch. This expansion per unit of measure may then bedivided by the number of units of temperature difference between theroom temperature at which the initial measurements were taken and theelevated temperature at which the second set of measurements were takento determine the CTE. This thermal expansion calculation may then beused to modify the original tool-path program to compensate for theeventual expansion of part 57 when brought to a process temperatureduring use.

At a step 76, the control of machine 1 may then implement the newtool-path program to further trim part 57 at room temperature. Trimmingpart 57 at step 76 may modify part 57 to compensate for CTE. Forexample, as a result of this second trimming, part 57 may assume theintended size and shape when heated to the intended process temperature.Later, when trimmed part 57 is heated to the intended processtemperature during use, part 57 may assume the intended shape and/orsize as it expands according to the calculated CTE.

Any steps of the process of FIG. 7 may be repeated one or more timesuntil the intended shape and/or size of the printed part to compensatefor CTE is achieved. The process may then end at step 77. While steps70-76 are depicted in a particular order, the principles of the presentdisclosure are not limited to the specific order shown in FIG. 7.

FIG. 8 depicts an exemplary method of using a surface scanner togenerate a new tool-path program to compensate for CTE. The exemplarymethod begins at starting step 84, during which an initial part 55(e.g., a thermoplastic mold or tool) may be formed via additivemanufacturing. Part 55 may be printed using printing gantry 23 of CNCmachine 1, as described above. The exemplary method may utilize atool-path program used for additive manufacturing using suitablesoftware, for example, CAD software, to manufacture part 55 to thedesired dimensions. In some aspects, part 55 may be printed at roomtemperature.

Once part 55 is printed, at a step 85, part 55 may be cooled orotherwise brought to room temperature, if it is not already at roomtemperature, and trimmed using trimming gantry 36 to create a trimmedprinted part 57. At a next step 86, trimmed part 57 may be scanned withan appropriate 3D surface scanning technology (e.g., 3D surface scanner68) at room temperature to measure trimmed part 57 along a plurality ofaxes. The measurement data may be then be transmitted from scanner 68 toa software program for storage, and a 3D rendition of part 57 at roomtemperature may be generated. Data from the computer software used totrim part 55 (e.g., CAD data) may also be sent to the software programfor storage in addition to, or instead of, data from scanner 68. Thesoftware program may be uploaded onto control of machine 1.

At a next step 87, trimmed part 57 may then be heated (e.g., using anoven, one or more heat lamps or heaters, or other suitable heatingdevice) to bring part 57 up to a desired process temperature. Heating oftrimmed part 57 may occur in place on CNC machine 1, or trimmed part 57may be moved for heating. In a next step 88, trimmed part 57 may bescanned once more using scanner 68, while part 57 is at the processtemperature. Measurement data for the heated, trimmed part 57 may betransmitted from scanner 68 to the software program, which may beuploaded on the control of machine 1. In some aspects, a 3D rendition ofpart 57 at the process temperature may be generated.

At a next step 89, the two sets of measurement data and/or 3D renditionsmay be compared, and the comparison may be used to generate a newtool-path program. In some examples, the software program, and/or thecontrol of machine 1, may perform this function by subtracting theinitial measurements at each measurement point taken when part 57 was ata cooler temperature from measurements taken at each measurement pointwhen part 57 was then heated to a process temperature to determine theamount of expansion at each measurement point. This expansion amount maythen be divided by the initial size measurement at each measurementpoint to calculate the expansion per unit of measure, for example, theexpansion per inch. This expansion per unit of measure may then bedivided by the number of units of temperature difference between theroom temperature at which the initial measurements were taken and theelevated temperature at which the second set of measurements were takento calculate CTE. This thermal expansion calculation may then be used tomodify the original tool-path program to compensate for the eventualexpansion of part 57 when brought to a process temperature during use.

At a step 90, the control of machine 1 may then implement the newtool-path program to further trim part 57 while at room temperature.Trimming part 57 at step 90 may modify part 57 to compensate for theCTE. For example, as a result of the second trimming, part 57 may assumethe intended size and shape when heated to the intended processtemperature. Later, when part 57 is heated to the intended processtemperature during use, part 57 may assume the intended shape and/orsize as it expands according to the calculated CTE.

Any steps of the process of FIG. 8 may be repeated one or more timesuntil the intended shape and/or size of the printed part to compensatefor CTE is achieved. The process may then end at step 91. While steps84-90 are depicted in a particular order, the principles of the presentdisclosure are not limited to the specific order shown in FIG. 8.

The CNC control may comprise one or more processors, one or more memorystorages, and/or one or more servers to achieve the aforementioned stepsin either FIG. 7 or 8.

From the foregoing detailed description, it will be evident that thereare a number of changes, adaptations, and modifications of the presentinvention that may come within the province of those persons havingordinary skill in the art to which the aforementioned disclosurepertains. However, it is intended that all such variations not departingfrom the spirit of the invention be considered as within the scopethereof.

What is claimed is:
 1. An additive manufacturing method, comprising:forming a part using additive manufacturing; measuring a first size ofthe part at a first temperature; bringing the part to a secondtemperature, different than the first temperature; measuring a secondsize of the part at the second temperature; comparing the first size tothe second size to calculate a coefficient of thermal expansion;bringing the part to the first temperature; and trimming the part usinga tool path that compensates for the coefficient of thermal expansion.2. The method of claim 1, wherein the second temperature is a processtemperature that the part will be heated to during use.
 3. The method ofclaim 1, wherein the second temperature is higher than the firsttemperature.
 4. The method of claim 1, wherein a touch probe is used tomeasure the part while the part is at the first temperature or thesecond temperature.
 5. The method of claim 1, wherein a scanner is usedto measure the part while the part is at the first temperature or thesecond temperature.
 6. The method of claim 1, wherein the trimming isperformed by a trimming gantry of a computer numeric controlled (CNC)machine.
 7. The method of claim 6, further including adjusting a scalingfactor of the CNC machine to compensate for the coefficient of thermalexpansion.
 8. An additive manufacturing method, comprising: forming apart using additive manufacturing; measuring the part along a pluralityof axes while the part is at a first temperature to determine a firstsize of the part; measuring the part along the plurality of axes whilethe part is at a second temperature, different than the firsttemperature, to determine a second size of the part; comparing the firstsize to the second size to calculate a coefficient of thermal expansionof the part along at least one axis of the plurality of axes; andtrimming the part, while the part is at the first temperature, tocompensate for the coefficient of thermal expansion.
 9. The method ofclaim 8, wherein a touch probe is used to measure the part while thepart is at the first temperature or the second temperature.
 10. Themethod of claim 8, wherein a scanner is used to measure the part whilethe part is at the first temperature or the second temperature.
 11. Themethod of claim 8, wherein the first temperature is a room temperature.12. The method of claim 8, wherein the forming and trimming areperformed using a computer numeric controlled (CNC) machine.
 13. Themethod of claim 12, wherein the trimming includes generating a programto modify a motion of the CNC machine to account for the coefficient ofthermal expansion.
 14. The method of claim 8, wherein the secondtemperature is lower than the first temperature.
 15. An additivemanufacturing method, comprising: forming a part using additivemanufacturing; measuring the part along a plurality of axes while thepart is at a first temperature to determine a size of the part at thefirst temperature; heating the part to a second temperature; measuringthe part along the plurality of axes while the part is at the secondtemperature to determine a size of the part at the second temperature;determining a coefficient of thermal expansion of the part based on thesize of the part at the first temperature and the size of the part atthe second temperature; generating a tool path of a computer numericcontrolled (CNC) machine to compensate for the coefficient of thermalexpansion; and trimming the part using the tool path while the part isat the first temperature.
 16. The method of claim 15, wherein the CNCmachine comprises a motor; and wherein trimming the part using the toolpath while the part is at the first temperature includes adjusting ascaling of the motor.
 17. The method of claim 15, wherein a touch probeis used to measure the part while the part is at the first temperatureor the second temperature.
 18. The method of claim 15, wherein a scanneris used to measure the part while the part is at the first temperatureor the second temperature.
 19. The method of claim 15, wherein the partis at least one of a tool or a mold, and wherein the second temperatureis a process temperature that the part will be heated to during use. 20.The method of claim 15, wherein forming a part using additivemanufacturing includes depositing material along a first tool path; andwherein generating a tool path of a CNC machine to compensate for thecoefficient of thermal expansion includes adjusting the first tool path.